Windows 7 - Suddenly 7 won't enter Sleep mode; start-up freezes

Windows 7 working fine on my Aspire pc 6 months; past few days, three problems have appeared;

1. won't enter sleep mode; the display turns black, but less than a minute later reappears showing same desktop programs running
2. after running an rkill/malwarebytes/superantispyware scan which was negative except for adware, I noticed 2 areas only of the display were flickering rapidly but were still visible; the trash can, and the up arrow on right end task bar which opens up the programs with messages, or just plain active; Windows update appears, flag appears if there's a message. when i click onto one of those program icons, they don't open up GUI
3. restart, the boot up is interrupted with a black background with 2 options; "Normal Windows 7 start", and "other options" with F8 or F10 showing repair, last safe start, etc. options for starting up. And, both those two options to select are flickering rapidly. if i select Windows Diagnostics, the result of that scan is everything working properly. If Normal start-up is selected, it does continue the normal boot up and works fine...but still won't go into sleep mode. and each re-start is the same; i have to select.

the only changes i recall are the rkill/malwarebytes/superantispyware scan, which i did just thinking good idea, as i'm going to change the Avira antivirus and the firewall freeware, for Norton Symantec 360. After running those scans, that's when i noticed the flickering and boot-up problem.

I did install some software but not within a day of these problems appearing.


I have noticed my 500 GB external hd has become too full to accept the weekly windows backup the past 2 sundays; and I don't understand how a system image copy, and one backup, can occupy almost 400GB on that drive...it has some music and video files also, leaving only 12 GB empty for the new backup. That seems wrong to me, for a single backup to take 400GB. there's not close to 400GB on the internal hd that's being backed up.
i'm attaching a Belarc review from November...
any ideas?
thanks! pdoyle